Dry/Wet Blend Pot

[downweverything]

Does anybody know of an easy way to add a dry/wet blend pot to any effect, so that it can be used with a bass.  I know there is the bass-thru schematic, but that is kinda large and it has a lot of parts.

[Peter Snowberg]

I love blend controls. Two ways you can do that are:

(1) Using a dual linear pot, take a dual op-amp wired up as two unity gain buffers, and use one half to buffer the effect output. Use the other half to buffer the signal applied to the effect input. Use the dual pot to blend between the outputs. Try blend pot values like 10K.

(2) Using a single pot, wire an opamp up like above, and feed each output to one end of a pot.

Some effects will invert the signal so one of the buffers must be changed to an inverting buffer.

I hope that helps.

Take care,
-Peter

[downweverything]

so using (2) do just take the input run it thru one unity buffer then connect its output to both the input of the effect and one side of the blend pot, then just hook the output of the effect thru another unity buffer then to the other end of the blend pot and the wiper of the blend pot becomes the new output and the input to the first buffer the new input?  is this correct?  would this be the best way to do it with a single blend knob.  i dont want more than one knob.

[smoguzbenjamin]

You'd just have one pot. turning it CCW would be dry and CW would be wet and halfway = 50/50 mix. I might do that for a few pedals I'm thinking of.

[Mark Hammer]

I put a blend pot on a Dr Quack for a bass-playing buddy for just such mixing, and it sounds wonderful.  Unfortunately, though, the filter section is inverting, relative to the input, so when you mix the dry signal with the filtered signal, you get cancellations.From a tonal perspective it sounds fine (and even more interesting than the stock unit) but the problem is that the mixing is passive, hence the effect signal is a bit weaker than the bypass signal.  :cry:

The moral is that such mixing is always possible, but attention should be paid to relative phase of the signals involved.  In this guy's case, he's using it in a studio situation so effect/bypass level matching is less critical.

[ethniccheese]

I've been wanting to build R.G.'s effect blender circuit for some time.  Has anyone else given this one a try?  It's on his "Panning for Fun" article.

[smoguzbenjamin]

Couldn't you use an inverting opamp at unity gain for the phase cancellations?

[Mark Hammer]

"Couldn't you use an inverting opamp at unity gain for the phase cancellations?"

Absolutely.  I was just drawing attention to the fact that in some cases, if you DON'T include such provisions, you get something different than what you expected.

[smoguzbenjamin]

Ah. Okidoke :mrgreen:

[sandro]

I love blend controls. Two ways you can do that are:

(1) Using a dual linear pot, take a dual op-amp wired up as two unity gain buffers, and use one half to buffer the effect output. Use the other half to buffer the signal applied to the effect input. Use the dual pot to blend between the outputs. Try blend pot values like 10K.

(2) Using a single pot, wire an opamp up like above, and feed each output to one end of a pot.



Some effects will invert the signal so one of the buffers must be changed to an inverting buffer.

I hope that helps.

Take care,
-Peter

Sorry, at the point 2) wasn't more correct saying "wire two op amp like above", or am I missing something? And, are some capacitors required somewhere in the circuit order to uncouple unwanted CC?

Thankyou for additional informations.